1. Field of the Invention
The present invention relates to a radar apparatus for an automobile attached to the body of the automobile, and an attachment direction adjuster and an attachment direction adjusting method for the radar apparatus.
2. Description of the Related Art
Conventionally, such a technique has been developed that a radar apparatus utilizing a radio wave or a laser beam is mounted on the body of an automobile thereby to search other vehicles etc. on a road on which the automobile runs (for example, see JP-A-Sho. 59-37471 and JP-A-Hei. 1-197684). In order to perform accurate search, it is necessary to make a searching range utilizing a radio wave or a laser beam narrow in a beam shape. When the search range is made narrow, at the time of attaching the radar apparatus for an automobile to the body of the automobile, it is required to adjust the radar apparatus so as not to deviate a beam axis in the vertical direction. When the beam axis deviates in the lower direction, only the road surface near the automobile is mainly searched. In contrast, when the beam axis deviates in the upper direction, an upper area away from the road surface is searched. Thus, unnecessary stationary objects such as a sign, signal, elevated road, which locate at higher positions and do not prevent the running of vehicles, are detected as obstacles and hence falling objects etc. on the road may not be searched. Although in most cases the horizontal direction is set as a reference direction of the beam axis, a direction slightly slanted from the horizontal direction is sometimes set as the reference direction. It is proved that an allowable range of the deviation of the beam axis is in a range of 1 to 2 degrees.
As methods of adjusting deviation of the beam axis in the lower and upper directions caused at the time of attaching the radar apparatus for an automobile to the body, there are known the following three methods, for example:
(1) a method of attaching the radar apparatus horizontally by using a spirit level,
(2) a method in which a search signal radiated from the radar apparatus is received by an antenna etc. disposed at a predetermined position in the forward direction of the automobile thereby to adjust the radar apparatus so that an output of the received signal becomes maximum, and(3) a method in which a reflection member is disposed at a predetermined position in the forward direction of the automobile so that a search signal radiated from the radar apparatus is reflected by the reflection member and the radar apparatus is adjusted so that an output of the reflection signal received by the radar apparatus becomes maximum. According to the method (1), the posture of the body of an automobile is kept horizontally, then a reference direction indicator such as a spirit level, which indicates the reference direction such as the horizontal direction based on the direction of the gravity of the earth, is placed on the reference surface set at the casing of the radar apparatus, and the attachment of the radar apparatus to the casing is adjusted so that the reference direction indicator indicates the reference direction.